Black widow spiders can detect a cannibal female from her web

Male black widow spiders can detect hungry, cannibalistic
females by the chemical and architectural make-up of their webs,
ecologists from Arizona State University have found.

Black
widow spiders (Latrodectus hesperus) got their name
thanks to this deadly quirk. The female critters are notorious for
finishing off mating with an after-sex-snack -- their male
partner.

But if they're nourished and well-fed, the female will
sometimes let her male mate off the hook. James Chadwick Johnson
and his team wanted to find out if the male spiders had the ability
to discern whether they would be cannibalised, before hopping into
the sack with a potential mate.

The ecologist team at Arizona's Johnson Lab kept a handful
of females hungry for several weeks, while the other group of
female black widows were fed with so many crickets that they almost refused the last few meals. They then
plopped bachelor male spiders onto the webs.

The male spiders were able to tell the difference as soon as they walked
onto the webs. The eight-legged animals can pick up scents through
their feet and can sense chemotactile cues in the webs. Web design gives clues too: nourished females make wide webs,
while starving ladyspiders make smaller webs with stickier
silk.

In the majority of cases, the male spiders carried out their
hours-long courtship dance more actively while on the web of a well-fed
gal, and tried to avoid the telltale signs of a hungry spider's
silk.

"We found that males courted well-fed females significantly
more than they did starved females," Johnson writes in the abstract of the study, which is presented in the
journal Animal Behavior. "This bias was maintained in the
absence of the female when males encountered only cues from female
webs."